[PATCH 07/13] mm: close race in generic_access_phys

[Jason Gunthorpe]

On Wed, Oct 07, 2020 at 08:01:42PM +0200, Daniel Vetter wrote:
> I think it'd fix the bug, until someone wires ->access up for
> drivers/gpu, or the next subsystem. This is also just for ptrace, so
> we really don't care when we stall the vm badly and other silly
> things. So I figured the somewhat ugly, but full generic solution is
> the better one, so that people who want to be able to ptrace
> read/write their iomem mmaps can just sprinkle this wherever they feel
> like.
> 
> But yeah if we go with most minimal fix, i.e. only trying to fix the
> current users, then your thing should work and is simpler. But it
> leaves the door open for future problems.

The only other idea I had was to fully make the 'vma of __iomem
memory' some generic utility, completely take over the vm_ops.

We did something like this in RDMA, what I found was even just
implementing mmap() using the kernel helpers turned out to be pretty
tricky, many drivers did it wrong in small ways.

Jason